Cathode ray tube having a conductive metallic coating therein

ABSTRACT

An improved color cathode ray tube of the shadow mask type is provided wherein localized areas of a primary conductive substance are disposed on the interior surface of the envelope funnel and neck portions separately covering the high voltage button and gun assembly contact areas. A substantially continuous secondary reflective coating of gas-sorbtive electrically conductive metallic material, providing advantageous life performance results, is disposed over the back surface of the shadow mask and over the interior surface of the funnel portion to provide a final anode coating effecting a peripheral unipotential field for the tube and electrically connecting the mask-screen area and the aforementioned localized primary coated areas. A thin tertiary film of high-efficiency gas-adsorbing getter material is disposed over at least a portion of the secondary conductive coating material.

United States Patent Benda et al.

[ CATHODE RAY TUBE HAVING A Primary Examiner-James W. LawrenceCONDUCTIVE METALLIC COATING Assistant Examiner-Saxfield Chatmon, Jr.THEREIN Arigriey Aglenti: or;i KNEE-[Norman J. OMalley; Ro-

a a t rc R 75 Inventors: David Benda, Geneva, N.Y.; Donald s 6 re R.Kerstetter, Emporium, Pa.

57 ABS A [73] Assignee: GTE Sylvania Incorporated, Seneca 1 TR CT Falls,Del. An improved color cathode ray tube of the shadow mask t e isrovided wherein localized areas of a ri- [22] Filed: June 1972 mary cgiiduc t ive substance are disposed on the inFer- [21] Appl. No.:263,297 ior surface of the envelope funnel and neck portionsseparatelycovering the high voltage button and gun assembly contact areas. Asubstantially continuous [52] Cl 313/85 a y/ 2 0 3 secondary reflectivecoating of gas-sorbtive electrisl 1 t Cl 6 29/46 cally conductivemetallic material, providing advanta- 85. geous life performanceresults, is disposed over the l 1 e 0 care 1 1 217 back surface of theshadow mask and over the interior surface of the funnel portion toprovide a final anode coating effecting a peripheral unipotential fieldfor the [56] References C'ted tube and electrically connecting themask-screen area UNITED STATES PATENTS and the aforementioned localized]primary coated ar- 2,093,699 9/1937 Varian et a]. 313/85 R eas. A thintertiary film of high-efficiency gas- 2.532,322 1/1952 Evans t 3/85 Radsorbing getter material is disposed over at least a 3279941 10/1966Foster at 313/174 X portion of the secondary conductive coatingmaterial. 3,432,712 3/1969 Benda 313/181 7 Claims, 2 Drawing Figures ll,33 H k 35 I I, 3 77 29 X,3| 25 i h F! 1 I r\ r 4 a5 68 I /1 23 s1 g 2 57I3 83 \v I f' s7 47 4 43 l 45 49 A j 1 CATIIODE RAY TUBE HAVING ACONDUCTIVE METALLIC COATING THEREIN BACKGROUND OF THE INVENTION Thisinvention relates to cathode ray tubes and more particularly to a colorcathode ray tube employing a substantially open metallic memberpositioned adjacent to the screen and having a metallic coatingdiscretely disposed therein to provide a final anode coating effecting aplurality of advantages for improving the life performance of the tube.

As conventionally manufactured, color cathode ray tubes of the typeemploying a multiple opening metallic member, such as a foraminousshadow mask or grid, positioned adjacent the patterned phosphor screen,usually have an extensive opaque coating of electrically conductivecolloidal graphite disposed on the interior surface of the envelopefunnel portion. This conductive graphite deposit, commonly referenced asAquadag, is applied to the funnel portion prior to tube assembly andsubsequently provides several functions in the finished tube. First, thefunnel covering material, being connected to the terminal anodeelectrode of the electron gun assembly, provides a continuation of theanode in the form of a final anode coating, whereof a peripheralunipotential field is established to surround the accelerated electronbeam as it is projected from the gun toward the screen. The extensiveapplication of the Aquadag coating affords a common means forelectrically connecting the high voltage button funnelconnection withthe terminal electrode of the electron gun and the mask-screen region ofthe tube. Further, this internal coating, in conjunction with aconductive coating. applied to the exterior surface of the funnelportion, forms a filter capacitor for the high voltage power supply.Additionally, this conductive internal coating provides shielding forthe electron beam or beams and prevents secondary emission charging ofthe glass of the envelope.

This graphite or Aquadag coating being extensively applied over theinternal surface of the funnel portion, sometimes tends to minutely peelor flake thereby releasing deleterious speck-like particles into theinterior 'of the finished tube. These contaminating particles arefree'to migrate to vulnerable regions of the tube, e.g., the screen areawhere they may be evidenced as minute but annoying overshadows, or tothe foraminous mask region where they may lodge blocking one or moreapertures therein, or to the region of the electron gun where theparticulate material may cause devastating leakage, arcs or shortsbetween electrodes. In addition to the loose particle shortcomings,application of the graphite coating to the interior of the funnelrequires a separate manufacturing procedure utilizing specializedapplicating equipment and labor, and as such adds to the manufacturingcosts of the tube.

OBJECTS AND SUMMARY OF THE INVENTION A It is an object of this inventionto reduce the aforementioned disadvantages and to provide an improvedcolor cathode ray tube having enhanced operational and life performancecharacteristics.

A further object is to produce a color cathode ray tube that evidences aminimum of loose particulate material therein.

Another object is to provide a color cathode ray tube having improvedefficiency for internal gas cleanup; the structure of which lends itselfto expeditious and economical fabrication procedures.

An additional objectis to provide an expeditious and economical methodfor manufacturing an improved color cathode ray tube.

The foregoing objects are achieved in one aspect of the inventionwherein an improved color cathode ray tube of, for example, the shadowmask type, has localized areas of a primary conductive substancedisposed on the interior surface of the envelope funnel and neckportions separately covering the high voltage connection and electrongun assembly contact areas. A substantially continuous secondaryreflective coating of gas-sorbtive electrically conductive metallicmaterial is applied over the interior surface of the shadow mask and theinterior surface of the funnel portion. This secondary coating overlaysand electrically connects the aforementioned areas of primary conductivecoating and provides the peripheral final anode coating for the tube. Athin tertiary film of a high-efficiency gasadsorbing getter material isdisposed over at least a por tion of the final anode coating ofconductive secondary material. An expeditious and economical method isprovided for fabricating an improved color tube wherein there is aminimum of loose particulate contaminate material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a shadowmask color cathode ray tube utilizing the invention; and

FIG. 2 is a perspective view of one type of material effusing structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding ofthe-present invention, together with other and further objlects,advantages and capabilities thereof, reference is made to the followingdisclosure and appended claims in connection with the above descriptionof some of the aspects of the invention.

With reference to the drawings, there is shown in FIG. 1, for example, ashadow-mask type of color cathode ray tube 11 having an envelope 13integrally comprising a face panel 15, a funnel portion 17, and a neckportion 19. A patterned cathode-luminescent screen 21 of selectedelectron responsive phosphor materials is formed on the interior surfaceof the face panel 15. To enhance the screen imagery, a film of aluminum22 is normally applied over the screen and the adjacent interior surfaceof the panel, such being accomplished by a vaporization procedure beforethe panel is attached to the funnel portion 17.

Adjacent to the screen and spaced therefrom is the I of which are shownas mating with compatibly oriented support studs 31 located in the wallor skirt 33 of the face panel member 15. The aforementioned aluminumfilm' 22 disposed on the interior of the panel also covers theprojecting support studs 31 thereby effecting electrical connectionbetween screen 21 and the adjacent shadow mask 23; The apertured member27 is formed of relatively thin metal such as, for example, low carbonsteel material having a thickness in the order of 0.005 to 0.006 of aninch. The multitudinous number of holes or apertures effect a masktransmission that is in the order of about 18 percent at the centerwhich may diminish to about 12 percent at the edge. Thus, the solid webof mask material 35 constitutes about 82 to 88 percent of the area ofthe apertured member 27.

Disposed within the neck portion 19 of the tube is the electron gunassembly 37 while not fully detailed as to structure, comprises'at leastone and usually two or more electron beam generating means. The pluralbeam convergence means 39, which is terminally oriented on the gunassembly, has a plurality of resilient support and connective means orsnubbers 41 that are formed to make contact with the interior of theneck portion 19. The electron gun assembly is further positionallysupported by a plurality of conductive pins (of which only four areshown) 43,44, 45, and 46 which traverse and are hermetically sealed inthe stemwafer closure member 47. This member, in turn, is integrallysealed to the open end of the neck portion 19. An exhaust tubulationincorporated in the closure member is shown as being hermetically sealed49 in the completed tube structure. Prior to sealing, this tubulation isconnected to a conventional vacuum or gas evacuation system, not shown,which is part of the tube processing procedure.

Disposed on" the interior surface of the funnel and neck portions 17 and19 are three discrete localized areas or patches of a primary conductivesubstance 53, for example, Aquadag or a suitable metallic material suchas a .gold, silver, or aluminum substance. One of the discrete areascovers the high voltage button region 55, extending substantiallyperimetrically therefrom to afford adequate areal contact with asubsequently applied metallic coating superjacently disposed thereover.A second area is disposed in substantially the neck-funnel transitionzone 57 of the envelope, in the region immediately forward of theelectron gun assembly 37 wherein the support snubbers 41 terminallyassociated with the gun assembly make electrical contact therewith. Thistransition-zone area 57 is usually in the shape of a substantiallyannular band forming a closed onductive loop. A third contact area 59 isdisposed on the forward region of the interior surface of the funnelportion 17 adjacent to the periphery of the shadow mask frame 25. Aresilient connective means 61 is attached to the mask frame and orientedin a manner to make a firm electrical connection with a portion of theadjacent contact area 59.

A secondary substantially continuous reflective coating 63 ofagas-sorbtive and electrically conductive metallic material, such as forexample, magnesium or magnesium alloy, is extensively andpredeterminately disposed over the interior or back surface of theshadow mask 23 and over substantially the whole of the interior surfaceof the envelope funnel portion 17. This extensive secondary metalliccoating, differing in composition from that of the primary conductivesubstance; provides several advantageous functions. Firstly, theconductive secondary coating overlays and electrically connects thebefore-described discrete primary coated substantially patch-like areas55, 57 and 59, extending therebeyond to cover the glass wall of thefunnel and thus provide a continuous final anode coating 60 for thetube. Secondly, this secondary exemplary magnesium coating isevaporatively applied to the interior surface after the cathode ray tubehas been exhaust processed. Such deposition provides a marked advantage,as during dispersal the magnesium is especially active in getteringresidual oxygen that may be present within the vacuous space of thetube. This beneficial gas-sorbing action, provided by the deposition ofthe final anode coating, improves tube performance by relieving thegas-sorbing load of the later-applied regular barium containing getter.Thus, a large portion of the regular gettering cpaacity is retained formaximum and longer gas-sorbing activity which is a promoting factor forlonger life performance of the tube. Thirdly, the exemplary magnesium,being flashed in the ambient vacuum of the tube, provides a highlyreflective mirrorlike coating on the interior surface of the shadowmask, and as such, acts as a heat radiator during tube operation. Thisreflective characteristic tends to lower the operating temperature ofthe mask thereby reducing the mask shift effect during tube operationthusly providing an added advantage to overall tube performance.

A secondary material giver or source, 67 from which the secondarygas-sorbing reflective and conductive coating is evaporated, may be inthe form of a stainless steel channelized ring or loop. One such giveris shown as attached to the frame 25 of the shadow mask 23 by suitablesupport means 68 and oriented in a manner to disperse the secondarycoating 63 over the interior of the funnel. Depending upon the size andshape of the funnel, two or more of such sources may be utilized toadequately achieve the uniform coverage desired. Additionally, in FIG.2, there is illustrated a channelized giver" 69 which is oriented, forexample, on a support 71 attached to the beam convergence means 39 ofthe electron gun assembly 37. Being so located, the evaporable material73, contained in the channel 75, is directed to cover the interiorsurface of the shadow mask, e.g., the interstitial webbing thereof inparticular.

There are instances in the prior art, in particularly monochrome cathoderay tubes, where metallic coatings of materials such as platinum,palladium, or aluminum were disposed on the interior surface of the tubeenvelope. Such deposition was usually achieved in the envelope per'se bya separate-step evaporization or sputtering procedure prior to tubeassembly since specialized high temperature vaporization sources wererequired. Thus, such metallic coatings, being priorly dispersed on theinterior of the envelope and subsequently exposed to atmosphere duringtube assembly, did not possess the efficient gas-sorbing andrearreflective characteristics as effected by the invention.

A thin tertiary film 77 of high-efficiency gas-sorbing getter material,such as barium or barium alloy, is disposed as a third layer over atleast a portion of the secondary or final anode coating 60. Usually,some of this getter film material 77 also deposits on the interior ofthe mask, but it also is highly reflective or mirror-like, beingevaporated in a vacuum environment. in FIG. 1, a conventional source ofgetter material 81 is shown positioned on an antenna-type support 83affixed to the electron gun assembly 37.

A method of fabricating the aforedescribed improved color cathode raytube comprises a plurality of related steps as ensuingly described.

The patterned cathodoluminescent screen 21 is formed on the interior ofthe face panel by tech niques familiar to the art, wherein the openingsin the spatially positioned shadow mask are utilized to produce thepatterned areas of the screen. Usually, the screened panel has a film ofaluminum 22 applied interiorly 'thereover by a separate step employingspecialized aluminizing equipment embodying a vacuum environment and ahigh temperature vaporization source.

The three discrete localized areas or patches 55, 57, 59 of primaryconductive substance 53, such as Aquadag, are applied to the aforenotedrespective regions of the envelope funnel and neck portions.

The shadow mask structure 23, with at least one giver or secondarymaterial source 67 attached thereto, is spatially positioned within thescreened and aluminized panel 15. The panel portion is then peripherallyfrit sealed, as at 85, to the lip of the funnel portion 17.

Next, the electron gun assembly 37 is inserted into the neck portion 19of the tube and the supporting closure member 47 is sealed to the openend thereof as at 87. The tube is then heated to substantially degas theenvelope l3 and the tube structural elements, e.g., 23 and 37, containedtherein. Simultaneously, the tube is evacuated of gases through theexhaust tubulation 48, shown in phantom as extending from the closuremember 47. Upon termination of processing the tubulation is hermeticallysealed as indicated at 49, which effects complete closure of theenvelope 13.

The secondary material source or sources 67 are activated by localizedinduction heating emanating from suitably energized coils orientedexteriorly of the envelope. This activation effuses the gas-sorbtiveelectrically conductive magnesium material into the interior of theenvelope in a manner to overlay the discrete pri- There is thus providedan improved color cathode ray tube that evidences a minimum of looseparticulate material, has improved efficiency for internal gas cleanup,exhibits enhanced operational and life performance characteristics, andone wherein the structure lends itself to expeditious and economicaltube fabrication procedures.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:

1. An improved color cathode ray tube having an envelope including facepanel, funnel and neck portions wherein a patterned cathodoluminescentscreen is disposed on the interior surface of the face panel with ametallic member having a multitude of openings therein positionedspatially adjacent thereto, and wherein at least one electron gun isoriented in said neck portion in a manner to beam electrons toward saidscreen, said improvement comprising:

a primary conductive substance disposed on the interior surface of saidfunnel and neck portions over at least two discrete localized areas, oneof said discrete areas covering at least the high voltage button areainthe funnel portion, and a second of said dis- Crete areas beingdisposed substantially in the neck-funnel transition zone of saidenvelope in the region immediately forward of said electron gun assemblywherein the terminal electrode of said gun assembly has associatedconnective means to make electrical contact therewith;

a secondary substantially uniform and continuous reflective coating ofgas-sorbtive and electrically conductive metallic material disposed overthe interior surface of said metallic member and substantially the wholeof the interior surface of said funnel portion overlaying the discreteareas of primary conductive coating thereon to provide a final anodecoating for the tube effecting means for establishing a peripheralunipotential field therein and electrically connecting said screen andmetallic member region and said afore-rnentioned first and seconddiscrete primary coated areas; and

a thin tertiary film of high-efficiency gas-sorbing getter materialdisposed over at least a portion of said final anode coating ofgas-sorlbtive electrically conductive secondary material.

2. The cathode ray tube improvement according to claim ll wherein saidsecond discrete area of said primary conductive substance is in theshape of a substantially annular band forming a closed conductive loop.

3. The cathode ray tube improvement according to claim 1 wherein saidsecondary gas-sorbtive electrically conductive metallic final anodecoating material is substantially magnesium.

4. The cathode ray tube improvement according to claim ll wherein athird localized discrete area of said primary conductive substance isdisposed on the for ward region of the interior surface of said funnelportion adjacent the periphery of said metallic member whereofconnective means associated with said pluralopening metallic membermakes electrical contact therewith.

5. The cathode ray tube improvement according to claim ll wherein saidprimary conductive substance is of a composition differing from that ofsaid secondary gas-sorbtive conductive metallic material.

6. The cathode ray tube improvement according to claim 1 wherein atleast one source of said secondary gas-sorbtive conductive metallicfinal anode coating material is oriented relative to said metallicmember.

7. The cathode ray tube improvement according to claim 1 wherein thepatterned cathodoluminescent screen formed on the interior surface ofsaid face panel has an aluminum film disposed thereover.

* =l =l l=

2. The cathode ray tube improvement according to claim 1 wherein saidsecond discrete area of said primary conductive substance is in theshape of a substantially annular band forming a closed conductive loop.3. The cathode ray tube improvement according to claim 1 wherein saidsecondary gas-sorbtive electrically conductive metallic final anodecoating material is substantially magnesium.
 4. The cathode ray tubeimprovement according to claim 1 wherein a third localized discrete areaof said primary conductive substance is disposed on the forward regionof the interior surface of said funnel portion adjacent the periphery ofsaid metallic member whereof connective means associated with saidplural-opening metallic member makes electrical contact therewith. 5.The cathode ray tube improvement according to claim 1 wherein saidprimary conductive substance is of a composition differing from that ofsaid secondary gas-sorbtive conductive metallic material.
 6. The cathoderay tube improvement according to claim 1 wherein at least one source ofsaid secondary gas-sorbtive conductive metallic final anode coatingmaterial is oriented relative to said metallic member.
 7. The cathoderay tube improvement according to claim 1 wherein the patternedcathodoluminescent screen formed on the interior surface of said facepanel has an aluminum film disposed thereover.